Polyester latex toners have been prepared utilizing amorphous and crystalline polyester latex. The incorporation of the polyester resin into toner requires that the polyester resin first be formulated into emulsions prepared by solvent containing batch processes, for example, solvent-based phase inversion emulsification (PIE). See, e.g., U.S. Pat. No. 8,192,913 and U.S. patent application Ser. No. 13/917,475, hereby incorporated by reference in its entirety. PIE is the procedure whereby the phases of a liquid-liquid dispersion interchange such that the dispersed phase spontaneously inverts to become the continuous phase and vice versa under conditions determined by the system properties, volume ratio and energy input. The phase inversion process involves the solubilization of resin and other components in an organic solvent such as methylethylketone (MEK). A phase inversion organic solvent is also added, which is typically chosen such that it is soluble with both the organic and aqueous phase, such as isopropanol (IPA).
There exist certain product specifications for the polyester resin to satisfy. For example, the solvent residuals are generally controlled to be less than 300 ppm by weight of the total weight of the polyester latex. Currently, companies are facing difficulties in efficiently removing the solvents from the polyester latex produced from the conventional PIE. One of the process challenges is to provide enough heat to evaporate the solvents, and another challenge is to provide effective mass transfer for the solvent evaporation to below a certain low solvent residual level, such as 50 ppm level. Specifically, co-solvent removal by distillation is difficult and time consuming. Some of the solvents that have good miscibilty with water, e.g., IPA, are particularly difficult to remove. In sum, the conventional PIE process is relatively time consuming, labor intensive, and has some lot-to-lot variability.
Significant amount of efforts and time have been invested in speeding up the emulsification and solvent removal processes, but satisfactory results have not been achieved. Therefore, a new emulsification process with significantly reduced cycle time and higher efficiency in co-solvent removal is highly desirable for overcoming the PIE process issues and thus achieving lower processing cost to make a polyester latex.